Another reputable source claims that the relaxed (flaccid, non-tumescent) human penis has an average length of only 4 inches (10 cm) and a diameter of 1.25 inches (3.2 cm) (which would result in a circumference of roughly 3.9 inches (9.9 cm) while fully erect ones have an average length of 6 inches (15 cm) and a diameter of 1.5 inches (3.8 cm), resulting in an erect circumference of 4.71 inches (12.0 cm).[8]